Flux plane locating in an underground drilling system

ABSTRACT

A portable locator and method are described for tracking the position of a boring tool and/or one or more buried lines within a region. In tracking a boring tool, a flux plane may be used to establish a flux vector as at least an intermediate step in guiding an operator of the portable locator to one or both locate points seen in the boring tool dipole locating field. The horizontal flux vector is used in determining a predicted locate point position. Locating of a locate line in the dipole locating field is performed by determining a predicted locate line angular orientation that is based upon horizontal flux vector determinations. The predicted locate line angular orientation, at least to an approximation, limits the possible directions to and orientations of a predicted locate line relative to the particular orientation of the portable locator at the above ground point. Cable line locating is performed by measuring a local flux intensity of the locating signal at a first above ground point within the region using a portable locator in a particular orientation. A cable line angular orientation is established which limits the possible directions to the cable line relative to the particular orientation of the portable locator. The portable locator display is configured for periodic updates such that displayed positional relationships are essentially continuous, including accommodation of positional and/or orientation changes seen by the portable locator in dipole or cable line tracking.

[0001] This is a continuation application of copending prior applicationSer. No. 09/641,006, filed on Aug. 17, 2000, the disclosure of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] The present invention relates generally to a system including anarrangement for tracking the position of a boring tool and/or one ormore buried lines within a region and, more particularly, to anarrangement for using certain characteristics of a dipole locatingsignal emanated from the boring tool and/or certain characteristics of alocating signal emanated from the buried lines to provide indications asto the locations of the boring tool and/or the in-ground lines.

[0003] The installation of utility lines underground using horizontaldirectional drilling equipment is increasingly popular for reasonsincluding elimination of the need to dig a trench. A number of prior artapproaches are available for the purpose of tracking the position of theboring tool within a region using a dipole locating signal that istransmitted from the boring tool. As one example, see U.S. Pat. No.5,633,589 entitled DEVICE AND METHOD FOR LOCATING AN INGROUND OBJECT ANDHOUSING FORMING PART OF SAID DEVICE (hereinafter the '589 patent) whichis commonly assigned with the present application and which isincorporated herein by reference. The '589 patent, like other prior artapproaches, utilizes a portable locating device to detect the locatingsignal for use in providing positional indications to an operator.

[0004] While the '589 patent holds a position representing a significantadvance in the field of boring tool locating and is, in fact, highlyaccurate and effective, it is submitted that there is room foradditional improvement. In particular, at least a minimum degree ofskill is required on behalf of an operator to obtain locating resultsthat are precise within some degree of tolerance. This skill requires,for example, some advance awareness and/or training regarding particularcharacteristics of the locating signal itself. In this connection, atleast some investment in operator training is required. Moreover,locating operations are slowed to some extent by requiring theapplication of procedures which insure accurate locating. Theseprocedures become more important in proportion to the level ofinexperience of an unskilled operator.

[0005] As one concern, it should be appreciated that in many regionsburied lines have previously been installed. When such lines arepresent, it is important to avoid damage caused by contact with theboring tool. In the past, operators often relied on pre-existinginformation as to the location of the lines provided, for example, by autility company or by locating services frequently provided by theutility company using simplistic locating devices and techniques. Thisconcern has been further elevated with the possibility of the presenceof fiber optic cables. In many instances, the lines are themselveselectrically conductive or, in the case of fiber optic cables, areconfigured with an electrically conductive tracer wire for use intransmitting a utility locating signal therefrom. It is submitted that aportable unit remains to be seen which facilitates boring tool and cablelocating in a single, convenient device.

[0006] The present invention provides a highly advantageous portablelocator and associated method which is submitted to resolve theforegoing concerns while providing still further advantages.

SUMMARY OF THE INVENTION

[0007] As will be described in more detail hereinafter, there isdisclosed herein a portable locator and associated method for trackingthe position of a boring tool and/or one or more buried lines within aregion.

[0008] In one aspect of the invention, the boring tool is moved throughthe ground within a given region along a path while transmitting alocating signal such that the locating signal exhibits locate points atthe surface of the ground, both ahead of and to the rear of the boringtool. A local flux intensity of the locating signal is measured for atleast one above ground point to establish a flux vector at that pointwhich is generally oriented in a horizontal plane. The orientation ofthe horizontal flux vector within the horizontal plane is used in apredetermined way which, at least to an approximation, limits thepossible directions of a nearest one of the locate points relative tothe above ground point.

[0009] In one feature, the orientation of the flux vector is used in thepredetermined way by displaying the orientation to an operator at theabove ground point to at least serve as an intermediate step in guidingthe operator to the locate point.

[0010] In another feature, the orientation of the horizontal flux vectorindicates two possible directions of the nearest locate point that areopposing with respect to the above ground point. The horizontal fluxvector is used in the predetermined way in combination with a verticalflux intensity of the locating signal that is established at the aboveground point from the measured local flux intensity to indicate a singleone of the two possible directions as the general direction of thenearest locate point.

[0011] In still another feature, with the portable locator in aparticular orientation, a positional relationship is displayed on theportable locator including the predicted location of the nearest locatepoint relative to the portable locator having a directional indicationsuch that the displayed directional indication points in the actualdirection of the predicted locate point from the initial above groundpoint.

[0012] In yet another feature, when the orientation of the portablelocator at the first above ground point is varied from the particularorientation, the portable locator displays an updated positionalrelationship such that the directional indication continuously points tothe predicted location, irrespective of a predetermined degree ofvariation of orientation of the portable locator.

[0013] In an additional feature, the portable locator is movediteratively to additional above ground points at which the display isupdated so as to indicate additional directional indications. Withsufficient iterations, the location of the predicted locate pointconverges with the actual locate point.

[0014] In another aspect of the present invention, a local fluxintensity of the locating signal is measured for at least one aboveground point to establish a flux vector at that point which is generallyoriented in a horizontal plane. An orientation of the flux vector isthen displayed to an operator at the above ground point to, at least inpart, serve in guiding the operator to at least one of the locatepoints.

[0015] In yet another aspect of the present invention, a boring tool ismoved through the ground within a given region along a path whiletransmitting a locating signal having a transmit axis such that thelocating signal exhibits locate points at the surface of the ground, oneof the locate points being ahead of the boring tool and the other one ofthe locate points being to the rear of the boring tool so as define avertical plane including the transmit axis along with a locate line thatis accessible at the surface of the ground and included in a locateplane which extends through the boring tool in a direction normal to thetransmit axis. An above ground point is established that is within aside locating region defined between a pair of planes one of whichextends through each locate point normal to the transmit axis. A localflux intensity of the locating signal is measured at the above groundpoint using a portable locator in a particular orientation. Using thelocal flux intensity, a predicted locate line angular orientation isestablished which, at least to an approximation, limits the possibledirections to and orientations of a predicted locate line relative tothe particular orientation of the portable locator at the above groundpoint.

[0016] In one feature, the predicted locate line may be in two possiblegeneral, but opposing directions from the above ground point. Thepredicted locate line angular orientation is used in combination with avertical flux plane slope of the locating signal, that is established atthe above ground point from the measured local flux intensity, toindicate a single one of the two possible general directions as thedirection of the predicted locate line.

[0017] In another feature, the portable locator is moved iteratively toadditional above ground points at which the display is updated so as toindicate additional positions of the predicted locate line. Withsufficient iterations, the location of the predicted locate lineconverges with the actual location of the locate line. In yet anotherfeature, crossing of the locate line is detected based on monitoring avertical component of flux intensity of the locating signal.

[0018] In still another aspect of the present invention, a first type ofpositional relationship is displayed to an operator at an above groundpoint including at least the position of the portable locator and anestimated position of one of a nearest one of the locate points to, atleast in part, serve in guiding the operator to at least the nearestlocate point using measured values of flux intensity of the locatingsignal. After finding at least the nearest locate point, the locator ismoved in a direction from the nearest locate point into an adjacent sidelocating region defined between a pair of planes one of which extendsthrough each locate point and each of which is normal to the transmitaxis. Based on a set of certain criteria within the adjacent sidelocating region, as the portable locator is moved therethrough, theportable locator is switched to a locate line display to display asecond type of positional relationship including at least the positionof the portable locator and an estimated position of the locate line. Inone feature, the locate line display is automatically presented based ondetection of flux lines produced by the locating signal in apredetermined range of flux slope orientation such that the portablelocator is, at least to an approximation, in proximity to the locateline. The predetermined range of flux slope orientation may bedetermined, at least in part, using a vertical component of theintensity of the locating field.

[0019] In an additional aspect of the present invention, a regionincludes at least one generally straight in-ground cable line extendingacross the region, from which cable line a locating signal istransmitted. The cable line is located by measuring a local fluxintensity of the locating signal at a first above ground point withinthe region using a portable locator in a particular orientation. Usingthe local flux intensity, a cable line angular orientation isestablished which limits the possible directions to the cable linerelative to the particular orientation of the portable locator at theabove ground point.

[0020] In one feature, a vertical flux slope orientation is establishedat the above ground point and an actual direction of the cable line isselected from the possible directions based on the vertical fluxorientation. The cable line is then displayed in a position relative tothe portable locator with the portable locator in its particularorientation.

[0021] In another feature, an updated positional relationship isdisplayed on the portable locator after moving the portable locator intoa new particular orientation to continuously indicate, at least towithin an approximation, the actual position of the cable line,irrespective of a predetermined degree of variation in orientation ofthe portable locator.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention may be understood by reference to thefollowing detailed description taken in conjunction with the drawingsbriefly described below.

[0023]FIG. 1 is a diagrammatic perspective see-through view of aportable locator that is manufactured in accordance with the presentinvention and shown here to illustrate its internal components.

[0024]FIG. 2 is a diagrammatic plan view of a region including anin-ground boring tool, shown here to illustrate the highly advantageouscharacteristics and use of horizontal flux lines which pass throughfront and rear locate points.

[0025]FIG. 3 is a diagramniatic elevational view of the region of FIG. 2showing the boring tool along with flux lines that are oriented in avertical plane along a transmit axis of the boring tool.

[0026]FIG. 4 is diagrammatic plan view illustrating the region of FIG. 1including contours of equal total magnetic flux intensity in ahorizontal plane, shown here to illustrate the close relative spacing ofthe contour lines along a locate line.

[0027]FIG. 5 is a diagrammatic view of the display of the portablelocator of FIG. 1, showing a horizontal flux vector based on the fluxlines seen in FIG. 2 for use in tracking the boring tool using thehighly advantageous flux plane technique of the present invention.

[0028]FIG. 5A is a diagrammatic view of the display of the portablelocator of FIG. 1, showing the location of a predicted locate pointahead of the current position of the portable locator illustrating thehighly advantageous and intuitive use of the flux plane locatingtechnique of the present invention.

[0029]FIG. 5B is a diagrammatic view of the display of the portablelocator of FIG. 1, showing the location of the predicted locate point ofFIG. 5A behind the current position of the portable locator furtherillustrating the highly advantageous and intuitive use of the flux planelocating technique of the present invention.

[0030]FIG. 5C is a diagrammatic view of the display of the portablelocator of FIG. 1, showing the location of the predicted locate point ofFIG. 5A at the current position of the portable locator such that thepredicted and actual positions of the locate point have merged uponhaving found the locate point through the operator having intuitivelymoved the locate point to the crosshair intersection.

[0031]FIG. 6 is a diagrammatic elevational view of the boring tool inthe locating region after having found the forward locate point shownhere for use in illustrating the determination of distance and depthvalues from the locate point. FIG. 7 is a diagrammatic plan view of theboring tool in the locating region shown here to illustrate sidelocating using a locate line which is shifted away from a positiondirectly above the boring tool at the surface of the ground when theboring tool is pitched.

[0032]FIG. 8 is a diagrammatic view, in elevation, showing the boringtool of FIG. 7 and further illustrating, in perspective, a pitch planethat is parallel to the transmit axis of the boring tool and whichcontains the locate line, illustrating further details with regard toside locating using the locate line.

[0033]FIG. 9A is the first figure in a series which diagrammaticallyillustrate the appearance of the display of the locator of the presentinvention during side locating with the predicted locate line ahead ofthe locator at the intersection of the crosshairs.

[0034]FIG. 9B is the second in the series of figures beginning with FIG.9A which illustrates the predicted locate line to the left of thelocator.

[0035]FIG. 9C is the third in the series of figures beginning with FIG.9A which illustrates the predicted locate line to the right of thelocator.

[0036]FIG. 9D is the fourth in the series of figures beginning with FIG.9A which illustrates the predicted locate line coextensive with ahorizontal one of the crosshairs such that a point along the locate linehas been found while the predicted position of the locate line hasmerged with the actual position of the locate line.

[0037]FIG. 10 is a diagrammatic plan view of a locating region includinga cable line, shown here to illustrate details of a locating signal thatis emitted by the cable line including the way in which the cable linelocating signal resembles the characteristics of a locate line exhibitedwithin a dipole locating field.

[0038]FIG. 11 is a diagrammatic elevational end view of the cable lineof FIG. 10 illustrating further details of the cable line locatingsignal.

[0039]FIG. 12 is a diagrammatic view of the display of the locator ofthe present invention shown here to illustrate the highly advantageoussimultaneous display of a cable line, a locate line and a locate point.

DETAILED DESCRIPTION OF THE INVENTION

[0040] Turning now to the drawings, wherein like items are indicated bylike reference numbers throughout the various figures, attention isimmediately directed to FIG. 1, which illustrates one embodiment of aportable locator, generally indicated by the reference number 10 andassembled in accordance with the present invention. Locator 10 includesa three-axis antenna cluster 12 measuring three orthogonally arrangedcomponents of magnetic flux in locator fixed coordinates. One usefulantenna cluster contemplated for use herein is disclosed by U.S. Pat.No. 6,005,532 entitled ORTHOGONAL ANTENNA ARRANGEMENT AND METHOD whichis co-assigned with the present application and is incorporated hereinby reference. A tilt sensor arrangement 14 is provided for measuringgravitational angles from which the components of flux in a levelcoordinate system may be determined. Locator 10 further includes agraphics display 16, a telemetry arrangement 18 having an antenna 19 anda microprocessor 20 interconnected appropriately with the variouscomponents. Other components (not shown) may be added as desired suchas, for example, a magnetometer to aid in position determinationrelative to the drill direction and ultrasonic transducers for measuringthe height of the locator above the surface of the ground.

[0041] Referring to FIG. 2 in conjunction with FIG. 1, a region 100 isshown including a boring tool 102 (indicated using a dashed line) whichtransmits a dipole locating field 104 that is received by antennacluster 12. Region 100 is shown in plan view. It is assumed that thesurface of the region is level and the boring tool is horizontallyoriented. These assumptions are made only for purposes of simplifyingthe present discussion and do not impose restrictions or limitations onthe applicability of the present invention in the absence of theassumptions. It is further assumed that boring tool 102 is oriented suchthat an arrowhead 106 points in a forward direction. Accordingly, aforward locate point 108 and a rear locate point 110 are present at ornear the surface of the region, as described, for example, in U.S. Pat.No. 5,337,002 entitled LOCATOR DEVICE FOR CONTINUOUSLY LOCATING A DIPOLEMAGNETIC FIELD TRANSMITTER AND ITS METHOD OF OPERATION which isco-assigned with the present application and is incorporated herein byreference.

[0042] Referring to FIGS. 1 and 2, using orthogonal antenna arrangement12, two components of the locating signal are established in ahorizontal plane, for example, along an x axis 112 oriented in alongitudinal direction along the locator's axis of symmetry 113 formeasuring a b_(x) component of locating field intensity and along a yaxis 114 for measuring a b_(y) component of locating field intensity. Athird component b_(z) is measured along a vertical, z axis 115. A seriesof flux lines 116 indicate the directional orientation of these fluxlines which are made up of only components of the locating signalintensity within the horizontal x-y plane of the figure. It is notedthat all flux lines in the horizontal plane (FIG. 2) pass through thelocate points. This latter characteristic of the locating field is animportant recognition, in accordance with the present invention, whichis relied on by locator 10, as will be further described. The x and yflux components needed to produce FIG. 2 may readily be determined usinglocator 10, for example, by insuring that the locator is level andoriented in a particular direction or by measuring all components usingantenna cluster 12 in a particular orientation (i.e., an x_(ant), ay_(ant) and a z_(ant) component that is orthogonal to thex_(ant)-y_(ant) plane) and determining the b_(x) and b_(y) componentswith reference to tilt and magnetic sensors.

[0043] Turning to FIG. 3 in conjunction with FIG. 2, the flux pattern ina vertical plane along drilling direction 106 is shown by FIG. 3 alongwith a locating direction 118 indicated by an arrow. At a locate point,the horizontal components of flux are zero such that the entire magneticflux is vertical. The flux lines in a vertical plane change slope at thelocate points as the locate point is passed. The boring tool is foundbetween the locate points. When the transmitter and the ground surfaceare both level (zero pitch, as illustrated), the boring tool is half wayin between the locate points on a level ground surface 119. Thehorizontal distances between locate points and the over-the-transmitterposition, directly above the boring tool, become unequal when thetransmitter is pitched. Another feature of the dipole magnetic field isa locate line 120 (FIG. 2) at which the magnetic flux lines in allplanes containing the transmitter axis are parallel to the transmitteraxis. Note that the locate line is also in a plane perpendicular to theaxis of the transmitter and, therefore, changes its position relative tothe ground surface with changes in transmitter pitch.

[0044] Still considering locate line 120, attention is directed to FIG.4 which illustrates region 100 including the total magnetic fluxintensity (total signal strength) in a horizontal plane at or above theboring tool, again assuming that the boring tool is at zero pitch. Aseries of contours 122 of total signal strength at different fixedlevels of signal strength are shown. The contours vary in magnitude ofsignal strength by an equivalent amount from one contour to the next. Itshould be noted that the contours are farther apart along a path in thedrilling direction as compared to their separation along locate line120, normal to the boring tool transmitter axis and drilling direction.Accordingly, it is recognized that the rate of change in signal strengthwith movement at the surface of the ground is greatest along the locateline. In this regard, it should be appreciated that the use of thelocate line is considered as being advantageous in light of thisrecognition, for example, in the side locating technique describedbelow.

[0045] Referring to FIGS. 1, 2 and 5, the directional orientation ofhorizontal flux lines 116 relative to locator 10 is determined usingb_(x) and b_(y) measured with respect to the axis of symmetry of theportable locator. FIG. 5 illustrates display 16 showing region 100 withlocator 10 at the origins of measured b_(x) and b_(y) intensity vectors.Accordingly, the tangent of an orientation angle α is defined as:

tan α=b _(y) /b _(x)  (1)

[0046] Therefore, with locator 10 at rest relative to the surface of theground, equation 1 can be used to display the orientation of a localhorizontal flux line 124 on display 16 of the locator. It should beunderstood that the locator's received flux line (FIG. 5) rotates whenthe locator is rotated about its vertical axis. As long as thetransmitter is at rest, however, the flux line does not move withrespect to the ground surface.

[0047] Still referring to FIGS. 1, 2 and 5, in and by itself, the useand/or display of local horizontal flux line 124 is considered to behighly advantageous. For example, displaying local horizontal flux line124 of FIG. 5 serves to limit the possible directions of the nearestlocate point relative to the position of the locator. In this regard, itshould be appreciated that local horizontal flux line 124 of FIG. 5represents the tangent to one of horizontal flux lines 116 shown in FIG.2. For any position of the locator within region 10, the localhorizontal flux vector or flux line may be considered to point to apredicted location of the locate point. Depending upon the position ofthe locator in the region, the predicted location represents the actuallocation of the locate point only to an approximation. Theseconsiderations are readily observed by noting the shape of thehorizontal flux lines in FIG. 2 and by bearing in mind that the locatordetermines the tangent at any position along one of flux lines 116. Thecloser the locator is to the locate point, the more accurately thetangent of the horizontal flux line points to the locate point. Uponactually finding a locate point, the horizontal flux components b_(x)and b_(y) go to zero (i.e., only the b_(z) component is non-zero at thelocate point) and directional indications are no longer defined.

[0048] Referring to FIGS. 2 and 5, using only the described feature ofobserving the local horizontal flux vector or flux line, identifying theposition of a locate point is relatively simple. That is, since x axis112 (FIG. 4) represents the axis of symmetry of the locator, theoperator of the locator may follow one of flux lines 116 by simplyrotating the locator until α is zero. That is, x axis 112 is alignedwith local horizontal flux vector 124. By maintaining this alignment, asat least an intermediate step, while continuously moving the locator inthe predicted direction of the locate point, the locator can follow oneor more of the flux lines directly to a locate point. In this regard, ithas been found that there is no requirement to follow a single one ofthe flux lines since the direction of a predicted location of the locatepoint is always indicated irrespective of being on any particular fluxline. This technique is particularly effective when the locator is inthe region between the locate points, as defined by a pair of sidelocating planes 126 that are oriented such that one plane passes througheach locate point and each is normal to the transmit axis of the boringtool.

[0049] Having generally described the flux plane locating feature of thepresent invention, attention is now directed to certain additionalfeatures which further enhance its use. It should be appreciated thatobserving local horizontal flux vector 124 provides no information as towhich direction along the flux vector is the correct direction toproceed in order to arrive at a locate point. That is, the flux vector,by itself, is ambiguous as to the actual direction of the nearest locatepoint along its directional orientation. In fact, if one were to followthe local flux vector initially away from the locate point outside ofside locating planes 126, one would never arrive at a locate point. Asdiscussed above, the technique will always bring one to a locate pointif one begins within the region between side locating planes 126.However, the locate point farthest from the initial position may be theone that is found first in the absence of additional provisions. While anumber of techniques may be used to indicate the direction in which toproceed along the local flux vector towards a nearest one of the locatepoints, one highly advantageous technique utilizes the verticalcomponent of intensity of the locating signal. More particularly, thevertical flux slope, as will be described immediately hereinafter.

[0050] Referring to FIG. 3, the slope of a flux line in a vertical planecan be defined as: $\begin{matrix}{{\tan \quad \beta} = {{- s}\quad i\quad g\quad {n\left( \frac{b_{x}}{b_{z}} \right)}{\sqrt{\left( \frac{b_{x}}{b_{z}} \right)^{2} + \left( \frac{b_{y}}{b_{z}} \right)^{2}}.}}} & (2)\end{matrix}$

[0051] Here, the vertical plane is assumed to be along the tangent ofthe horizontal flux line at any particular location in region 100. Thesign of angle β depends on locating direction and on locator positionrelative to the locate points (and locate line). As an example, βbecomes positive when the user is ahead of the forward locate point,pointing the locator in the direction of the boring tool transmitter(i.e., facing the boring tool transmitter in locating direction 118). Asdescribed above, the true direction from locator to locate point cannotbe determined based on the measurement of the flux vector at one pointof the magnetic locating field. Since all horizontal flux lines gothrough the locate points, however, one can just follow a flux line toultimately find a locate point, accepting the attendant 180 degreeambiguity. The use of β, however, serves to resolve this concern.Similarly, the true distance to a locate point can also not bedetermined based on available data obtained at a single point, but theangle β can serve as a practical indication of the distance to thelocate point. By combining the described elements including the use ofthe local horizontal flux vector and the use of β, a highly advantageousand heretofore unseen technique is provided.

[0052] By using the technique described immediately above, the operatorcan progressively move toward the locate point. After moving to a newabove ground point in the direction of a new predicted location of thelocate point along the direction defined by the horizontal flux vectorat the current location of the portable locator, a new local fluxintensity is measured at the new above ground point. At the new aboveground location, the locator then indicates a new direction based on thelocal horizontal flux vector. Once again, the operator moves inaccordance with the indications. Ultimately, the operator will arrive atthe locate point after repeating this process a sufficient number oftimes, as the predicted location of the locate point converges on itsactual position. At each progressive location, the use of the verticalflux slope is used to provide the indication as to which of the twodirections of the local flux vector is toward the locate point. If theoperator passes the locate point, the locator will indicate thatmovement in the opposing direction along the local flux vector isnecessary.

[0053] With each successive measurement, the locator displays apositional relationship including the predicted location of the nearestlocate point relative to the locator, with a directional indication,such that the directional indication points in the actual direction ofthe predicted location of the locate point from an initial or subsequentabove ground point. Moreover, it should be appreciated that if thelocator is held at one above ground point in varying orientations, thelocator will display an updated positional relationship which accountsfor variation in the orientation so as provide a directional indicationwhich continuously points in the actual direction of the predictedlocation of the locate point, irrespective of a predetermined degree ofvariation in the orientation. That is, within an approximation,depending upon the frequency with which the display is updated. Using astate of the art microprocessor, an update rate of approximately 15positions per second is readily achieved in locate point indication aswell as in other tracking implementations to be described. Thus, thepositional relationship is continuous insofar as the perceptions of theoperator of the portable locator are implicated, accounting for positionand/or orientation changes experienced by the locator. As will befurther discussed, this locating technique has been found to beremarkably effective in the hands of an operator with virtually noexperience due to the intuitive nature of the display provided by thelocator. Specific displays utilizing the foregoing concepts will beprovided immediately hereinafter.

[0054] Turning to FIG. 5A, display 16 is illustrated including a set ofcrosshairs 130 at the intersection of which the locator of the presentinvention is positioned, as indicated by a virtual locator box 10′. Thevertically oriented crosshair is oriented along the axis of symmetry ofthe locator. Hence, the upward direction in the figure represents deadahead to the operator of the portable locator. In essence, this displaypresents a “picture” of the operational region to the operator whichshows his location at the center relative to a predicted direction anddistance of a locate point. The predicted location of a nearest locatepoint is indicated by a target symbol 134. The latter may be connectedto the crosshair intersection by a line 136 (representing the local fluxline) for purposes of emphasizing the predicted direction of the locatepoint. The display of FIG. 5A is provided when β>0. In this instance,the locate point will be ahead of the locator, above the horizontalcrosshair, with its predicted direction indicated by the localhorizontal flux vector (i.e., the tangent to the local horizontal fluxline given by equation 1). The distance to the predicted location of thelocate point is proportional to |β|. That is, β is zero at the locatepoint and increases with increasing distance from the locate point.

[0055] Referring to FIG. 5B, display 16 is illustrated with thepredicted location of the locate point behind the portable locator. Inthis instance, β<0 such that locate point target symbol 134 is shown inthe lower part of the display below the horizontal crosshair. Similarly,distance is based upon the magnitude of β.

[0056] Referring to FIG. 5C. display 16 is illustrated in the instancein which the locate point has been reached. Thus, β is equal to zero andtarget symbol 134 is moved to the center of crosshairs 130. Asmentioned, in applying this locating procedure, the operator need notfollow the same flux line to the locate point. Instead, the operator mayswitch over to any convenient flux line which allows moving the locatepoint target symbol to the center of the display crosshairs. Finding alocate point is as simple as putting a “ball in the box”. In actualtesting, the disclosed technique has proven to be remarkably simple andeffective. Moreover, the technique has proven to be so intuitive thatlocator 10 has been handed to a person with no knowledge or training inlocating techniques and that person has used locator 10 to proceedforthwith directly to a locate point.

[0057] Referring to FIG. 6, boring tool 102 is shown pitched in region100. Having reached a locate point, a projected transmitter depth D anda horizontal distance S at the surface of the ground from the locatepoint to an overhead point, OH, directly above the boring tooltransmitter are obtained from measured flux and transmitter pitch usingthe following equations:

D=r sin(α′+φ)  (3)

s=r cos(α′+φ)  (4)

[0058] where r is a radial distance between the boring tool transmitterand the locate point, φ is the boring tool transmitter pitch, and α′ isthe angle formed between the axis of symmetry of the boring tooltransmitter and radius r.

[0059] where $\begin{matrix}{r^{3} = \frac{4}{{{- b}\quad \sin \quad \varphi} + {b\sqrt{8 + {\sin^{2}\varphi}}}}} & (5) \\{{\tan \quad \alpha^{\prime}} = {\frac{4}{{3\tan \quad \varphi} + \sqrt{8 + {9\tan^{2}\varphi}}}.}} & (6)\end{matrix}$

[0060] It is noted that b denotes the total locating signal strength ata locate point. When using these equations, if transmitter pitch is notzero, it is necessary to distinguish between the forward and rear locatepoint. For use at the forward locate point, the equations are used aswritten. For the rear locate point, however, the sign of transmitterpitch φ must be reversed. Pitch is generally measured by a sensor in theboring tool transmitter with the pitch data being modulated on thedipole locating signal. It is also worth mentioning that usefuldeterminations can be performed when the horizontal distance from alocate point to the over-the-transmitter position is known, for example,in determining or double checking depth, D. A precise overhead locationcan be determined in one way by monitoring total signal strength, whichreaches a maximum above the boring tool transmitter.

[0061] Referring again to FIG. 2, it should be appreciated that thereare situations in which locate points cannot be reached. In thesesituations, the boring tool must be found in an alternative way. Inother situations, the operator my find a locate point, but is stillunable to walk to a position above the boring tool transmitter. Perhapsthe boring tool is beneath a river or some sort of structure. In any ofthese situations, locate line 120 may provide valuable guidance since itis possible that the operator will have access to at least some portionof the locate line.

[0062] Referring to FIGS. 7 and 8, characteristics of the locatingsignal with regard to the locate line will now be described. FIG. 7 is aplan view showing boring tool 102 in region 100. FIG. 8 is anelevational view showing boring tool 102 at a pitch φ. The surface ofthe ground is not shown for purposes of clarity. A flux line 150 isillustrated which passes through a point A (FIG. 8) on locate line 120.It should be observed that locate line 120 is shifted in position at thesurface of the ground due to the nonzero pitch value such that thelocate line does not pass directly over the boring tool. As the pitchchanges, locate line 120 moves at the surface of the ground. A fluxvector 152, obtained from a reading taken at point B (offset on thelocate line from point A) and on a different flux line (not shown),includes an intensity and directional orientation, as indicated. Thelocate line is itself contained in a pitch plane 156 (FIG. 8) that isparallel to axis 157 of the boring tool transmitter. Thus, the pitchplane is normal to any plane which is itself normal to the transmitaxis. It should be appreciated that, if the pitch is zero, pitch plane156 is horizontal and parallel to a horizontal ground surface. Fluxvector 152 is resolved in two orthogonal directions in the pitch plane,which directions are designated by the components b_(x) _(p) and b_(y)_(p) . In the instance of a zero pitch value, the b_(x) _(p) componentis equal to the component b_(x) determined along x axis 112 in FIG. 1while the b_(y) _(p) component is equal to the component b_(y)determined along y axis 114. Where the pitch plane is not horizontal,the b_(x) _(p) component is in vertical alignment with the b_(x)component. In other words, b_(x) _(p) projects directly onto b_(x)within the horizontal x-y plane with the x axis being the axis ofsymmetry of locator 10. The b_(x) _(p) and b_(y) _(p) values are readilydetermined using pitch φ, b_(x) and b_(y).

[0063] A predicted locate line orientation angle γ is formed betweenpitch plane flux vector 152 and b_(y) _(p) . Knowing b_(x) _(p) andb_(y) _(p) :

tan γ=b _(x) _(p) /b _(y) _(p)   (7)

[0064] Using the predicted locate line angular orientation, γ, locateline 12 is displayable as a line normal to the flux line (at point B) inpitch plane 156 (FIG. 8), as will be seen. A measure for the distance tothe locate line may be based upon flux component b_(z) _(p) , normal tothe pitch plane. This distance is thus proportional to $\begin{matrix}\frac{b_{z_{p}}}{\sqrt{b_{x_{p}}^{2} + b_{y_{p}}^{2} + b_{z_{p}}^{2}}} & (8)\end{matrix}$

[0065] While the estimated distance and directional orientation are nowknown, it should be appreciated that two possible, but opposingdirectional ranges are defined. In other words, it is unknown whetherthe locate line is in one general direction from the locator or inexactly the opposite direction. Vertical flux slope orientation, β,determined using equation 2 is useful in combination with the predictedlocate line angular orientation in selecting which of the two opposingdirections is toward the actual predicted locate line.

[0066] Further considering the use of vertical flux slope orientation inthe present context, because flux b_(z) _(p) changes sign at the locateline, this information is useful in triggering the side locating orlocate line display. It should be noticed that the described featuresare sufficient to approach the locate line at any angle and to follow itto the transmitter or a reference point when side locating so long asthe locator is between side locating planes 126 of FIG. 2. In thisregard, it should be appreciated that the determined position of thelocate line is a predicted location. As the locate line is approached,the actual position of the locate line converges with the predictionlocation since the relationship defined by equation 7 gives the correctorientation for values measured only at the locate line. Therefore, thistechnique is similar to that discussed above for finding a locate point.That is, the direction of the locate line with respect to the portablelocator is correct within an approximation, depending upon the distancebetween the locate line and the locator such that viewing theorientation of the predicted locate line establishes a general directiontoward the predicted locate line. The side locating technique of thepresent invention is also performed in an iterative manner in order toapproach the actual locate line. After beginning at some initial pointwithin the side locating region, the locator is moved toward thepredicted locate line. The display will then be updated at a new aboveground point to indicate a new predicted locate line in a neworientation based on new readings of the local flux intensity. Theoperator then proceeds in the direction of the new predicted locateline. With sufficient iterations, the positions of the actual locateline and the predicted locate line will converge. Specific displaysutilizing the foregoing locate line technique will be describedimmediately hereinafter.

[0067] Referring to FIGS. 9A-9D, a series of locate line displays ispresented which diagrammatically illustrate the appearance of display 16on locator 10 (FIG. 1). FIG. 9A illustrates the appearance of display 16including a predicted locate line 160 at a distance from the portablelocator that is estimated, for example, using equation 8. Again, theposition of the portable locator in the display corresponds to theintersection of crosshairs 130. In the example of FIG. 9A, the predictedlocate line is directly ahead of the portable locator vertically upwardand skewed in the figure. The dead ahead direction, along the axis ofsymmetry of the portable locator, is emphasized by an arrowhead 162.

[0068]FIG. 9B illustrates the appearance of display 16 in the instancewhere predicted locate line 160 is generally to the left of the portablelocator. The operator, in proceeding with the intent of finding thelocate line, will intuitively orient the portable locator such that thepredicted locate line is dead ahead. It should be appreciated that thisside locating technique is highly advantageous in the manner of the fluxplane technique described for locating locate points, as describedabove. That is, a display is presented which illustrates to the operatorthe actual direction in which to proceed toward the predicted locationof the locate line. Moreover, the predicted location of the locate lineis updated at a predetermined interval such that changes in theorientation of the portable locator (i.e., those changes that include arotational component about a vertical axis) result in a new, updatedpresentation on display 16 so as to illustrate the actual direction inwhich the operator should proceed on a continuously updated basisirrespective of orientation and/or position changes to which the locatoris subjected. Again, the display is continuous insofar as the perceptionof the operator is concerned.

[0069]FIG. 9C illustrates display 16 with predicted locate line 160generally to the right of the position of the portable locator.Accordingly, the operator will turn to the right, towards the predictedlocation, which will result in a display resembling that of FIG. 9A.

[0070]FIG. 9D illustrates display 16 having predicted locate line 160coinciding with the horizontal one of crosshairs 130. Having achievedthis display, the position of the predicted locate line has converged onthe actual location of locate line 120 (FIG. 2). Therefore, the operatorhas succeeded in finding a point on the locate line. Using thisinformation, the operator may continue side locating by continuing totrack the locate line, for example, as the boring tool passes beneath astructure or rock formation.

[0071] Because the aforedescribed technique for finding and displayingthe locate line is useful only in the region between planes 126 whichdefine the side locating region, a number of different methods may beutilized in order to ensure that the operator is within this region. Themethods can be employed individually or in combination. Three of thesemethods are described immediately below.

[0072] In a first method, a locate point is first found, for example,using the flux plane technique described above. Thereafter, the operatorproceeds in any direction while monitoring the signal strength of thelocating signal while verifying that the signal strength is increasing.If the signal strength decreases, the operator should return to thelocate point and try a new direction. By monitoring for an increase insignal strength, it is assured that the operator is moving into the sidelocating region defined between side locating planes 126 of FIG. 2.

[0073] In a second method, the aforedescribed angle β is used to monitorprogress toward the locate line. Upon approaching the locate line, βapproaches either +90 or −90 degrees. When β is within a pre-selectedrange, the locator is in the vicinity of the locate line at least to afirst approximation. That is, the measurement error in displaying thepredicted locate line is within a corresponding range. In fact, oneimplementation contemplates automatically presenting a locate linedisplay when β enters this pre-selected range. Alternatively, theoperator may be notified on display 16 that the locate line display isavailable for use. The operator may then press a button to manuallyactuate the locate line display mode. As another alternative, the locateline display may automatically be triggered upon detection that thelocate line has been crossed. This is particularly useful in the casewhere the tan β expression of FIG. 2 changes signs. In this instance,the display would then show the predicted locate line behind the locator(i.e., below rather than above the horizontal one of crosshairs 130 inFIG. 9A).

[0074] In a third method, the positions of both of the locate points areestablished. The side locating region resides between the locate points,as described above. Having established the locate point positions, theoperator may proceed with the side locating technique of the presentinvention at any point within the side locating region. It should beappreciated that many variations are possible in presenting a locateline display in view of the foregoing teachings. Accordingly, all ofthese variations are considered as falling within the scope of thepresent invention so long as the disclosed teachings are applied.

[0075] Having described the highly advantageous features of the presentinvention for establishing locate point positions and for performingside locating, it is important to understand that these features may beintegrated within the same portable locator. An overall highlyadvantageous method is thereby implemented which permits displaying afirst type of positional relationship to an operator at an above groundpoint including at least the position of the portable locator and anestimated position of one of the locate points. This display serves to,at least in part, guide the operator to at least the nearest locatepoint using measured values of flux intensity of the locating signal.After finding the nearest locate point, or both locate points, theportable locator is moved in a direction from the nearest locate pointinto the adjacent side locating region defined between the side locatingplanes, one of which extends through each locate point and each of whichis normal to the transmit axis. Thereafter, as the locator is moved inthe side locating region, a set of certain criteria is monitored withinthe side locating region for actuating purposes. When the criteria aresatisfied, for example, in the aforedescribed manners includingdetection of readings within a predetermined range of flux slopeorientation, switching to the locate line display is performed todisplay a second type of positional relationship including at least theposition of the portable locator and an estimated position of the locateline.

[0076] While the described locating procedure and display features allowdetection of the position and orientation of an underground transmitter,detection of an underground utility consisting, for example, of a powercable, a telephone line, a pipeline or any other obstacle with animbedded active tracer wire is performed in a highly advantageous way.This type of locating is referred to hereinafter as cable line locating.In locating a boring tool, described above, the transmitter emits adipole-type magnetic field. In contrast, the current in the tracer wireof a cable line produces a two-dimensional magnetic field, as will befurther described.

[0077] Referring to FIGS. 10 and 11, a region 170 is shown including acable line locating field 172 surrounding a cable line 174 beneath ahorizontal ground surface 175. It should be appreciated that cable linelocating field 172 is much less complex than the magnetic dipolelocating field seen in the methods and examples appearing above. Forpurposes of simplicity, cable line 174 is illustrated in a horizontalorientation, however, this is not a requirement.

[0078] Still referring to FIGS. 10 and 11, it is assumed that the cableline is relatively straight over a distance large compared to its depthbeneath the surface of the ground. Accordingly, FIG. 11 shows that cablelocating field 172 is two-dimensional, characterized by a pattern ofcircular flux lines 176 in planes normal to the tracer wire whichpattern repeats along the cable line. The flux lines immediately abovethe cable line are normal to its plan-view in FIG. 10, as indicated by aflux vector 178. Further, a vertical component of flux intensity, b_(z)(FIG. 11), changes sign at the overhead position directly above thecable line. That is, b_(z) is zero at the overhead position, and istherefore illustrated offset from the overhead position, but has adifferent sign on either side of the overhead position. Clearly, thesecharacteristics of a cable line are related to those of a locate line sothat the locate line procedure, described above, is also generallyapplicable in cable line locating. In this regard, the cable line doesnot exhibit a side locating region which advantageously furthersimplifies the overall cable line locating procedure. The presentexample also considers a horizontally oriented cable line which istypically the case. Further, the instant procedure is directlyapplicable without modification to a slanted cable line.

[0079] Still referring to FIGS. 10 and 11, cable line locating signal172 is resolved into horizontal flux components b_(x) and b_(y). Theformer is once again the locate direction that is defined by the axis ofsymmetry of portable locator 10. In the instance in which the particularorientation of the portable locator is not horizontal, these componentvalues are readily determined, for example, using a tilt meter readingtaken within the portable locator.

[0080] A cable line orientation angle γ′ is formed between flux vector178 and b_(y). Knowing b_(x) and b_(y):

tan γ′=b _(y) /b _(x)  (9)

[0081] Using the cable line angular orientation, γ′, locate line 12 isdisplayable as a line normal to flux line 178. In this regard, it shouldbe appreciated that the cable line angular orientation differs withrespect to the aforedescribed side locating procedure in that the cableline orientation angle represents the actual directional orientation ofthe cable line, rather than a predicted direction. Like side locating, a180 degree angular ambiguity is also present. A measure for the distanceof the cable line may be based upon flux component b_(z), normal to thepitch plane. This distance is thus proportional to $\begin{matrix}\frac{b_{z}}{\sqrt{b_{x}^{2} + b_{y}^{2} + b_{z}^{2}}} & (10)\end{matrix}$

[0082] With the estimated distance and an ambiguous directionalorientation now known, the directional ambiguity is resolved usingvertical flux slope orientation, β, determined using equation 2.Further, considering the use of vertical flux slope orientation in thecable line context, because flux b_(z) changes sign at the locate line,this information is useful in indicating passing across an overheadpoint directly above the cable line. Like a locate line, the cable linecan be approached at any angle and followed thereto. The cable locatingtechnique of the present invention is also performed in an iterativemanner in order to find the cable line. After beginning at some initialpoint, the locator is moved toward the indicated cable line. The displaywill then be updated at a new above ground point to indicate a newposition of the cable line in a new orientation based on new readings ofthe local flux intensity. The operator then proceeds in the direction ofthe new cable line location. With sufficient iterations, the cable linewill be found.

[0083] Specific displays utilizing the cable line locating technique ofthe present invention are not provided since these displays may beessentially identical to the side locating displays seen in FIGS. 9A-9D,described above. As in the case of side locating using this displayform, the operator, in proceeding with the intent of finding the cableline, will intuitively orient the portable locator such that thepredicted cable line is dead ahead. Moreover, the display presentedillustrates to the operator the actual direction in which to proceedtoward the location of the cable line. Like the side locatingimplementation, the displayed location of the cable line is updated at apredetermined interval such that changes in the orientation of theportable locator, including a rotational component about a verticalaxis, result in a new, updated presentation on display 16 so as toillustrate the actual direction in which the operator should proceed ona continuously updated basis. As mentioned above, this display featureis operative with respect to position and/or orientation changesexperienced by the locator and is, for practical purposes, continuous atthe contemplated update rates.

[0084] Turning to FIG. 12, the cable line locating feature andassociated display may be used alone for cable line locating or may beintegrated with the locate point and/or locate line locating features.FIG. 12 illustrates display 16 with a combination of all three forms oflocating “objects” displayed. Specifically, a cable line 180 isrepresented by a solid line, a predicted locate point 182 is illustratedas a dot and a predicted locate line 184 is shown as a dashed line. Allof these are indicated in relation to a “virtual” locator 10′. To avoidmisinterpretation, the cable line symbol on the display of the portablelocator differs from the appearance of the locate line. Textual labelsmay also accompany any of the illustrated items. By simultaneouslyshowing both the cable line and transmitter data, the portable locatorof the present invention provides a powerful tool for use in avoidingthe hazards of drilling into underground utilities while guiding aboring tool.

[0085] A number of possible approaches may be used in order for thelocator to distinguish between the signal from the boring tooltransmitter and one or more buried cable lines. For example, a differentfrequency may be used for each item being located or tracked. The sametri-axial receiving antenna 12 (see FIG. 1) may be used to receive allthe employed frequencies. A digital signal-processing receiver is usedto extract the signal amplitudes for each antenna and frequency.Alternatively, different sets of receiving devices may be used. In anycase, a microprocessor is configured for processing the data fordisplay. In the case of AC power cables, the signal naturally emanatingfrom the AC cable may be used as the cable locating signal. If more thanone cable is present, however, a different frequency for each cable maybe employed. The location data for each cable may be presented alone orin combination with the location data for other cables.

[0086] One alternative to multiple frequency use is the use of timemultiplexed signals that are synchronized at the locator. Suchmultiplexing may be used for the cable lines in the ground or mayinclude the boring tool transmitter as well. Combinations of multiplefrequencies and time multiplexing are also contemplated.

[0087] Because the portable locator and associated method disclosedherein may be provided in a variety of different configurations andmodified in an unlimited number of different ways, it should beunderstood that the present invention may be embodied in many otherspecific forms without departing from the spirit or scope of theinvention. For example, the present teachings are applicable to any typeof locating which utilizes a dipole locating field or a cable line typelocating field. Therefore, the present examples and methods are to beconsidered as illustrative and not restrictive, and the invention is notto be limited to the details given herein, but may be modified withinthe scope of the appended claims.

What is claimed is:
 1. In an overall system in which a boring tool ismoved through the ground within a given region along a path whiletransmitting a locating signal such that the locating signal exhibitslocate points at the surface of the ground, both ahead of and to therear of the boring tool, a method comprising the steps of: a) measuringa local flux intensity of the locating signal for at least one aboveground point for use in establishing a horizontal flux vector at thatpoint which is generally oriented in a horizontal plane; and b) movingin a direction generally defined by the orientation of the horizontalflux vector as at least an intermediate step in establishing theposition of a nearest one of the locate points.
 2. The method of claim 1further comprising the steps of: c) at a new above ground point in saiddirection generally defined by the orientation of the horizontal fluxvector, measuring a new local flux intensity to establish a newhorizontal flux vector having a new orientation in the horizontal plane;and d) moving in a new direction along the new horizontal flux vector.3. The method of claim 2 wherein the horizontal flux vector is definedalong an initial flux line and the new horizontal flux vector is definedalong a new flux line that is different than the initial flux line suchthat more than one flux line is used in moving toward the boring tool.4. The method of claim 1 wherein the boring tool is orientedhorizontally, said method further comprising the steps of: c) at thenearest locate point, measuring a locate point value of the fluxintensity; d) using the measured locate point value of the fluxintensity, estimating the horizontal distance of the nearest locatepoint from the boring tool as well as the depth of the boring toolbeneath the surface of the ground.
 5. The method of claim 1 wherein theboring tool may exhibit pitch in moving underground, said method furthercomprising the steps of: c) measuring the pitch of the boring tool; d)at the nearest locate point, measuring a locate point value of the fluxintensity; e) using the measured value of the locating field and thepitch, estimating the horizontal distance, S, of the boring tool fromthe nearest locate point and the depth, D, of the boring tool beneaththe surface of the ground.
 6. The method of claim 5 wherein D and S aredetermined by the expressions D=r sin(α′+φ), and s=r cos(α′+φ) where φis pitch, b is a total flux intensity obtained from the measured localflux intensity and where r and α′ are determined by${r^{3} = \frac{4}{{{- b}\quad \sin \quad \varphi} + {b\sqrt{8 + {\sin^{2}\varphi}}}}},{a\quad n\quad d}$${\tan \quad \alpha^{\prime}} = {\frac{4}{{3\tan \quad \varphi} + \sqrt{8 + {9\tan^{2}\varphi}}}.}$


7. In an overall system in which a boring tool is moved through theground within a given region along a path while transmitting a locatingsignal such that the locating signal exhibits locate points at thesurface of the ground, both forward of and to the rear of the boringtool, a portable locator comprising: a) a first arrangement formeasuring a local flux intensity of the locating signal for at least oneabove ground point for use in establishing a horizontal flux vector atthat point which is generally oriented in a horizontal plane; and b) asecond arrangement for indicating a direction generally defined by theorientation of the horizontal flux vector for use in establishing theposition of a nearest one of the locate points.
 8. The portable locatorof claim 7 wherein the boring tool is oriented horizontally and whereinthe portable locator further comprises: c) a third arrangement for usingthe measured local flux intensity taken at the nearest locate point toestimate the horizontal distance of the locate point from the boringtool as well as the depth of the boring tool beneath the surface of theground.
 9. The portable locator of claim 7 wherein the boring tool mayexhibit pitch in moving underground and wherein the portable locatorfurther comprises: c) a third arrangement for using the measured localflux intensity taken at he nearest locate point in combination with thepitch for estimating the horizontal distance of the boring tool from thenearest locate point and the depth of the boring tool beneath thesurface of the ground.